Motor overload detection with predetermined rotation reversal

Abstract

An apparatus is provided for controlling an electric motor that is doing some sort of work, whereby the apparatus automatically senses the presence of a work overload. Once the work overload is sensed, the apparatus automatically reverses the direction of rotation of the motor to eliminate the work overload. The reversed rotation is limited to either a predetermined period of time or to a predetermined number of reverse rotations. Once the predetermined limit of reverse rotation is reached, the apparatus automatically resumes normal rotation of the motor.

What is claimed is: 
     
       1. An apparatus for reversing the direction of rotation of a motor from normal operation and for restoring the normal direction of rotation, comprising: means for detecting current load utilized by the motor during normal rotation,   means for comparing the current load utilized by the motor during normal rotation with a predetermined current load utilization level representative of a work overload,   means, responsive to said current load comparing means, for automatically reversing the direction of motor rotation when the current load utilized by the motor during normal rotation exceeds the predetermined current load utilization level, reverse rotation serving to eliminate the work overload,   means for automatically limiting the amount of reverse rotation of the motor, said motor reversing means being responsive to said reverse rotation limiting means, whereby said motor reversing means are automatically restored to normal operation in response to said reverse rotation limiting means, whereby the motor is automatically restored to rotate in the normal direction of rotation.   
     
     
       2. The apparatus described in claim 1, wherein said reverse rotation limiting means include means for timing a predetermined length of time for permitting reverse rotation, whereby said means for reversing direction of motor rotation are responsive to said timing means. 
     
     
       3. The apparatus described in claim 1, wherein said reverse rotation limiting means include means for providing a measurement signal representative of the amount of reverse rotation, means for providing a reference signal representative of a predetermined amount of reverse rotation, and means for providing a comparison signal representing a difference between said measurement signal and said reference signal, whereby said means for reversing direction of motor rotation are responsive to said comparison signal. 
     
     
       4. The apparatus described in claim 1, wherein said reverse rotation limiting means include means for providing a signal representative of the amount of reverse positioning of a driven load, whereby said means for reversing direction of motor rotation are responsive to said reverse positioning signal. 
     
     
       5. The apparatus described in claim 1, wherein the motor is a DC motor. 
     
     
       6. The apparatus described in claim 1, wherein the motor is an AC motor. 
     
     
       7. An apparatus for reversing the normal direction of DC motor rotation when the motor encounters a work overload and for restoring the normal direction of rotation after the work overload is eliminated, comprising: means for monitoring DC current load utilized by the motor during normal rotation,   means for comparing the current load utilized by the motor during normal rotation with a predetermined current load utilization level representative of a work overload,   means, responsive to said current load comparing means, for automatically reversing the direction of motor rotation when the current load utilized by the motor during normal rotation exceeds the predetermined current load utilization level, reverse rotation serving to eliminate the work overload,   means for automatically limiting the amount of reverse rotation of the motor including means for providing a measurement signal representative of the amount of reverse rotation, means for providing a reference signal representative of a predetermined amount of reverse rotation, and means for providing a comparison signal representing a difference between said measurement signal and said reference signal, whereby said means for reversing direction of motor rotation are responsive to said comparison signal for automatically restoring the motor to rotate in the normal direction of rotation.   
     
     
       8. An apparatus for reversing the direction of rotation of a DC motor from normal operation when encountering a work overload and for restoring the normal direction of rotation when the work overload is eliminated, comprising: means for monitoring DC current load utilized by the motor during normal rotation,   means for comparing the current load utilized by the motor during normal rotation with a predetermined current load utilization level representative of a work overload,   means, responsive to said current load comparing means, for automatically reversing the direction of motor rotation when the current load utilized by the motor during normal rotation exceeds the predetermined current load utilization level, the reverse rotation serving to eliminate the work overload,   means for automatically limiting the amount of reverse rotation of the motor, said motor rotation reversing means being responsive to said limiting means, said limiting means including means for timing a predetermined length of time of reverse rotation whereby the motor is automatically restored to rotate in the normal direction after the expiration of said predetermined length of time.   
     
     
       9. An apparatus for reversing the normal direction of DC motor rotation when the motor encounters a work overload and for restoring the normal direction of rotation after the work overload is eliminated, comprising: means for monitoring DC current load utilized by the motor during normal rotation,   means for comparing the current load utilized by the motor during normal rotation with a predetermined current load utilization level representative of a work overload,   means, responsive to said current load comparing means, for automatically reversing the direction of motor rotation when the current load utilized by the motor during normal rotation exceeds the predetermined current load utilization level, reverse rotation serving to eliminate the work overload,   means for automatically limiting the amount of reverse rotation of the motor including means for providing a signal representative of a predetermined amount of reverse positioning of a driven load, said means for reversing direction of motor rotation being responsive to said reverse positioning signal, whereby the motor is automatically restored to rotate in the normal direction after said predetermined amount of reverse positioning.   
     
     
       10. An apparatus for reversing the normal direction of AC motor rotation when the motor encounters a work overload and for restoring the normal direction of rotation after the work overload is eliminated, comprising: means for monitoring AC current load utilized by the motor during normal rotation,   means for comparing the current load utilized by the motor during normal rotation with a predetermined current load utilization level representative of a work overload,   means, responsive to said current load comparing means, for automatically reversing the direction of motor rotation when the current load utilized by the motor during normal rotation exceeds the predetermined current load utilization level, reverse rotation serving to eliminate the work overload,   means for automatically limiting the amount of reverse rotation of the motor including: means for providing a measurement signal representative of the amount of reverse rotation, means for providing a reference signal representative of a predetermined amount of reverse rotation, and means for providing a comparison signal representing a difference between said measurement signal and said reference signal, said means for reversing direction of motor rotation being responsive to said comparison signal whereby the motor is automatically restored to rotate in the normal direction of rotation after said predetermined amount of reverse rotation.   
     
     
       11. An apparatus for reversing the direction of rotation of an AC motor from normal operation when encountering a work overload and for restoring the normal direction of rotation when the work overload is eliminated, comprising: means for monitoring AC current load utilized by the motor during normal rotation,   means for comparing the current load utilized by the motor during normal rotation with a predetermined current load utilization level representative of a work overload,   means, responsive to said current load comparing means, for automatically reversing the direction of motor rotation when the current load utilized by the motor during normal rotation exceeds the predetermined current load utilization level, the reverse rotation serving to eliminate the work overload,   means for automatically limiting the amount of reverse rotation of the motor, said limiting means including means for timing a predetermined length of time of reverse rotation, whereby the motor is automatically restored to operate in the normal direction of rotation after the expiration of said predetermined length of time.   
     
     
       12. An apparatus for reversing the normal direction of AC motor rotation when the motor encounters a work overload and for restoring the normal direction of rotation after the work overload is eliminated, comprising: means for monitoring AC current load utilized by the motor during normal rotation,   means for comparing the current load utilized by the motor during normal rotation with a predetermined current load utilization level representative of a work overload,   means, responsive to said current load comparing means, for automatically reversing the direction of motor rotation when the current load utilized by the motor during normal rotation exceeds the predetermined current load utilization level, reverse rotation serving to eliminate the work overload,   means for automatically limiting the amount of reverse rotation of the motor including means for providing a signal representative of a predetermined amount of reverse positioning of a driven load, said means for reversing direction of motor rotation being responsive to said reverse positioning signal, whereby the motor is automatically restored to rotate in the normal direction of rotation after said predetermined amount of reverse positioning.